I've also noted folks who spend significant time on both in big cities with public transport, and also significant time in car-centric cities, their weight fluctuates appropriately (about 15% less weight when decent public transport is available).
I live on the south coast of the UK and I take the bus to work and then walk home in the evening, takes about an hour. It's pretty pleasant and a good way to both process the day and move around a little. I feel far better when I walk home than when I used to take the bus.
It's actually one thing I'm slightly bugged by as I'm getting ready to move to the bay area for a year. I don't want to buy or lease a car. I haven't actually wanted or needed a car since getting my licence.